Emitter Flow & Dripper Discharge q = k·Hˣ
Drip PC
A dripper's discharge follows q = k × pressure^x, where the exponent x shows how pressure-compensating it is. Enter the constant, exponent and operating pressure to get the discharge in litres per hour.
Enter your emitter
Next: multiply 1.9 L/h by the number of emitters per plant and per zone to size your system flow, and keep the exponent low (≈0.5) if your field has elevation change so output stays uniform.
Emitter law: q = k × H^x, with H in metres of head.
Emitter flow — key facts
- Discharge
- q = k × pressure^x (L/h)
- Exponent x
- flow sensitivity to pressure
- x ≈ 0
- pressure-compensating
- x ≈ 0.5
- turbulent-flow emitter
- x ≈ 1.0
- orifice / long-path
- Constant k
- discharge coefficient
- Working pressure
- ≈ 0.5–1.5 bar
- Privacy
- Runs in your browser; nothing uploaded
Pressure sets the flow — and the exponent says by how much
Every drip emitter discharges according to q = k × pressure^x. The constant k scales the flow, while the exponent x is the real story: it says how strongly flow tracks pressure. An exponent near one means flow climbs almost in lockstep with pressure, so emitters at different points on a line water unevenly. An exponent near zero is a pressure-compensating emitter, holding a steady flow across a wide pressure range — exactly what long runs and sloping fields need.
This tool gives the emitter discharge in litres per hour, the constant k, the exponent x and the operating pressure from the discharge equation. Use it to compare emitters, set regulator pressure and design uniform laterals. Pair it with the Drip Zone Scheduling, Irrigation Set Volume and Water Hammer tools for a full irrigation plan.
Read the exponent
See how pressure-compensating an emitter really is.
Set the pressure
Find the discharge at your regulator setting.
Design uniform lines
Pick a low x for long or sloping laterals.
Compare emitters
Test k and x side by side before you buy.
Frequently Asked Questions
How is emitter discharge calculated?+
By the emitter discharge equation q = k × H^x, where q is the flow in litres per hour, H is the operating pressure, k is the emitter's discharge coefficient and x is its discharge exponent. The tool raises the pressure to the power x and multiplies by k to give the discharge at your operating pressure.
What does the exponent x tell me?+
The exponent x measures how sensitive the emitter's flow is to pressure. An x near 1.0 means flow rises almost in step with pressure — a simple long-path or orifice emitter. An x near 0 means flow barely changes as pressure varies — a fully pressure-compensating emitter. The lower the x, the more uniform the discharge along a line with pressure differences.
What is a pressure-compensating emitter?+
A pressure-compensating (PC) emitter has a flexible diaphragm that throttles the flow path as pressure rises, holding the discharge nearly constant over a working pressure range. Its discharge exponent x is close to zero, often 0.0–0.2. PC emitters give uniform watering on long runs, sloping ground and undulating terrain where pressure varies along the lateral.
What is a typical emitter exponent?+
Orifice and long-path emitters usually have x around 0.5–0.7; turbulent-flow emitters around 0.5; and pressure-compensating emitters around 0.0–0.2. Manufacturers publish k and x for each model, or you can fit them from two flow-versus-pressure measurements. The lower the x, the flatter the flow curve.
Why does emitter flow uniformity matter?+
Uniform discharge means every plant gets the same water, which drives even growth and efficient use. Pressure always drops along a lateral due to friction, and rises or falls with slope, so emitters at different points sit at different pressures. A low exponent keeps their flows close despite that, which is why PC emitters are chosen for long or sloping lines.
What pressure should I run the emitter at?+
Use the manufacturer's recommended operating pressure, typically 0.5–1.5 bar (about 5–15 m of head) for drip emitters. Running below the range under-waters and can let emitters drain unevenly; running above wastes energy and, for non-PC emitters, over-applies. The tool lets you test the discharge across the range before you set the regulator.
Can I find k and x from measurements?+
Yes. Measure the discharge at two different pressures, then x = ln(q2/q1) ÷ ln(H2/H1), and k = q1 ÷ H1^x. With k and x in hand, this tool predicts the discharge at any pressure in the working range, which is handy when a catalogue value is missing or you want to verify an emitter in the field.
Does emitter discharge change as the line clogs?+
Yes — clogging from sediment, biofilm or precipitates raises the effective flow resistance and lowers discharge below the q = k·H^x curve, and it does so unevenly across emitters. The equation describes a clean emitter; declining or patchy flow in the field is a sign to flush the lines and check filtration. Regular maintenance keeps real flows close to the calculated value.
Are the figures precise?+
They are accurate for the k and x you enter, which are the manufacturer's published or field-fitted values. Real discharge varies a little with water temperature, manufacturing tolerance between emitters and clogging over time. Use the result for design and pressure setting, and verify with a catch test on a sample of emitters in the field.